The invention relates to a method for recording data on a magnetic recording medium wherein data signals output by a data source are coded in a coder stage and the coded data signals are supplied to a write amplifier which emits write signals to a data head for recording the data on the data recording medium. The invention also relates to an arrangement for the implementation of the method.
In recording data on a magnetic recording medium, for example a magnetic tape or a magnetic disk, it is already generally known to supply data signals allocated to the record data to a coder stage which generates coded data signals, and to supply these to a write amplifier. The write amplifier generates write-in signals which are usually fashioned as write currents which are proportional to the coded data signals. Numerous writing methods, for example the NRZI, the MFM, or the GCR writing method are available for coding the data signals.
When the write currents are supplied directly to a write head in the magnetic head, the magnetization of the recording medium corresponds to the chronological curve of the write currents. This method is generally referred to as a direct recording method. The implementation of this method is extremely simple, but it exhibits various disadvantages. When no premagnetization is employed and the write signal is the only excitation of the recording medium, the recording process is nonlinear and the recording sensitivity is low. A relatively high write current is required in order to magnetize the recording medium up to its saturation, and this results in the fact that modulation signals and cross-talk occur to a high degree.
When the recording density is increased, the signal-to-noise ratio is also deteriorated and a shift of the rated point in time of the peaks of the read signals occurs, this being generally referred to as "bit shift". The principal reason for the peak shift lies in the a-symmetry of the magnetization of the recording medium, which depends on the appearance of the binary characters 0 and 1 in the data signals. This results from the fact that the recording medium is magnetized up to its saturation in both directions, and the remanence on the recording medium is a function of the spacing between two successive magnetization changes. The magnetization of the recording medium between two magnetization changes is redundant as viewed from the standpoint of data storage, and represents a principal reason for the peak shift.
The read output signals have a maximum at that location at which the magnetic flux exhibits its greatest positive slope, and have a minimum at that location at which the magnetic flux exhibits its greatest negative slope. These points are employed in order to recover the data, and it is standard to differentiate the read output signals and to teen identify the successive zero axis crossings. Consequently, these locations have the same degree of peak displacement as is present in the magnetization of the recording medium. Every differentiation of the magnetic flux is connected with an increase of noise, which means that the signal-to-noise ratio is lower than is maximally prescribed by the magnetization.
German OS No. 32 33 489, corresponding to U.S. Pat. No. 4,547,818, incorporated herein by reference, discloses that the write signals can be superimposed with high-frequency premagnetization signals and can be supplied to the magnetic head. The recording medium is alternately magnetized up to its saturation by the pre-magnetization signals having a frequency which lies far above the pass band of the read channel.
As a result of employing pre-magnetization signals, the recording process is linearized and a more precise recording thus occurs. The recording sensitivity becomes greater, which means that a corresponding magnetization can be achieved with a significantly lower write current. The advantage is that fewer modulation signals and less cross talk appear in the read channel.